Download The Heart

9/25/13
Collin County Community College
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BIOL. 2402
Anatomy & Physiology
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WEEK 5
The Heart
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(1578-1657) A groundbreaking work in the history of medicine, English physician
William Harvey s Anatomical Essay on the Motion of the Heart and
Blood in Animals named the heart as the organ responsible for pumping
blood. He also was the first one to propose that CVS is a closed circuit.
Although criticized when first published in 1628, Harvey s work was soon
accepted by scientists and laid the groundwork for modern physiology.
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The Heart and the CVS
The heart is the pump that
propels the blood through a
closed circulatory system
Blood cells never leave this
circulation !
Red color indicates blood that
isfully oxygenated.
Blue color represents blood
that is only partially
oxygenated.
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The Heart and the CVS
The heart is actually a dual
pump
•  Right side of the heart
functions to propel blood
through the pulmonary
circulation
•  Left heart propels blood
through the systemic
circulation
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The Heart and the CVS
Main purpose of the heart is to generate blood flow and blood
pressure
One of the key functions is to provide the distant tissues with
energy so that they can function .
C6H12O6 + 6O2
6CO2 + 6H20 + 38 ATP
Exchange of nutrients and gases occurs at the capillary level.
•  5 % of total blood volume resides in the capillary beds.
•  Other 95 % of blood volume , with the heart and blood vessels, is
involved in generating a pressure / flow system through the
conduit.
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Heart Anatomy
Area between the two pleura is called the mediastinum
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Heart Anatomy
Parietal pericardium
Epicardium
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Heart Anatomy
Visceral pericardium
(epicardium)
Parietal pericardium
Pericarditis :
Inflammation of the
pericardium
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Heart Anatomy
Heart has two upper atria
and two lower ventricles.
(Expandable exterior portion of an
atria is called the auricle)
Right atrium connects to
right ventricle and left
atrium connects to left
ventricle.
There is no direct
connection between left
side and right side.
Blood vessels leaving the
heart are arteries/aorta
Blood vessels arriving at
the heart are veins
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Heart Anatomy
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Heart Anatomy and Blood flow
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Major Blood Vessels at the Heart
Major blood vessels of the heart include
•  Inferior and superior
vena cavae
•  Pulmonary trunk (splits
into pulmonary arteries)
•  Pulmonary veins
•  Aorta
•  Brachiocephalic
•  Left common carotid
•  Left subclavian
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Blood flow and Heart valves
The heart valves make sure that blood flows only in one direction
They prevent backflow and also allow pressure to build up bt
creating a closed system
Atrio-Ventricular valves are located between the atria and ventricles
•  Left AV-valve or Bicuspid Valve (Mitral valve)
•  Right AV - valve or Tricuspid valve
•  Remember LAB-RAT
Semi-lunar valves are located between ventricles and blood-vessel
that guides blood out of the ventricle
•  Aortic semi-lunar valve between left ventricle and aorta
•  Pulmonary semi-lunar valve between right ventricle and
pulmonary artery
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Blood flow and Heart valves
AV valves are connected
to ventricular walls at the
papillary muscles via the
chordae tendineae !
They prevent the valves
to flip open against the
direction of the blood flow.
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Blood flow and Heart valves
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Blood flow and Heart valves
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Blood flow and Heart valves
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Blood flow and Heart valves
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Blood flow and Heart valves
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The Heart wall
Components of the heart wall include
•  Epicardium = visceral pericardium
•  Myocardium = actual cardiac muscle mass
•  Endocardium
= thin lining of endothelial cells that
lines inside 21
The Heart wall
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The Heart wall
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Left and Right Ventricular Heart Wall
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Microscopic Heart Cell Anatomy
Cardiac cells have similar arrangement as striated
skeletal cells, with some obvious differences
• cells are connected via gap-junctions and
desmosomes
• have sarcomeres with A-I band arrangement of
actin/myosin
•  20-25 % of cell volume taken up by mitochondria
(compare with 2% in skeletal muscle)
•  less T-tubules and SR
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Microscopic Heart Cell Anatomy
Cardiac muscle
includes most
of the structures
seen in skeletal
muscle,
including
the striated
arrangement
of actin and
myosin.
Adjacent myocarial cells are connected by intercalated disks,
which have desmosomes for strength, and gap junctions
for the coordination of contraction during pumping.
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Microscopic Heart Cell Anatomy
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Blood Supply to the Heart
Cardiac muscle requires its own blood supply to
provide the oxygen and necessary nutrients.
This is done by the coronary blood vessels.
•  Arteries include
• the right and left coronary arteries,
• anterior and posterior interventricular arteries,
• and the circumflex artery
•  Veins include
• the great cardiac vein,
• anterior and posterior cardiac veins,
• the middle cardiac vein, and the small cardiac vein
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Blood Supply to the Heart
Coronary arteries
originate at the base of
the aorta.
Posterior Coronary veins
drain into the coronary
sinus, which empties into
the right atrium.
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Blood Supply to the Heart
CAD = coronary artery disease
Ischemia = reduced circulatory supply
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Blood Supply to the Heart
Angina pectoris = temporary ischemia develops
during increased workload on the
heart ( such as exercise)
Medication :
•  sympathetic blockers (propranolol)
•  Vasodilators ( nitroglycerin)
•  Calcium blockers
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Autorhythmic Activity of the Heart
The Heart has the property of being able to contract without
impulses from the nervous system.
This auto-rhythmic property is due to the presence of
specialized cell that fire action potentials at a certain rhythm.
•  Main pacemaker center is called the Sino Atrial (SA) node,
located in the upper part of the right atria
•  Electrical impulses are picked up by the AtrioVentricular Node
and conducted via the Bundle of His down the intraventricular
septum and the left and right bundle branches.
•  Finally, electrical impulses are conducted up the walls of the
ventricles via the Purkinje fibers.
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Autorhythmic Activity of the Heart
The heart s
pacemaker and
conducting
system are shown
in bright yellow.
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Autorhythmic Activity of the Heart
The sinoatrial node is
the heart s pacemaker
because it initiates
each wave of excitation
with atrial contraction.
The Bundle of His and other parts
of the conducting system deliver
the excitation to the apex of the
heart so that ventricular contraction
occurs in an upward sweep.
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Autorhythmic Activity of the Heart
This electrical discharge by the
autorhythmic cells provides a
neat coordinated process with
the contractile activity of the
cardiomyocytes, which in turn
provides the heart beat, blood
flow and blood pressure.
This sweep of electrical activity
across the heart is at the basis
of the electrocardiogram (ECG
or EKG).
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The Heart Beat
Two types of cells are
involved in a normal
heart beat.
•  the autorhythmic cells
(depolarize with a
certain rhythm)
•  the cardiomyocytes
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The Heart Beat and action potentials
What ionic events occur during a normal action
potential in a nerve or skeletal muscle cell ?
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The Heart Beat: AP s in the pacemaker cells
The action potential of an
autorhythmic cardiac cell.
The rhythmic aspect is
due to an unstable resting
membrane potential called
the pacemaker potential or
pre-potential.
When it reaches threshold
it result in an action
potential.
What causes this prepotential to drift ?
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The Heart Beat: AP s in the pacemaker cells
Unstable prepotential is due
to closure of K+ channels
and brief opening of funny
channels that slowly let more
Na+ in.
Funny channels close and
T-calcium briefly open and
close.
At threshold, L-type
Calcium open, resulting in
depolarization.
L-type Calcium channels
close and K+ channels
open, resulting in re39
polarization.
The Heart Beat: the conducting cells
ParaSympathetic activity :
•  ACh increases K+ permeability
during the prepotential drift.
•  Prolongs the time to reach
threshold ; HR slows down
Sympathetic activity :
•  NE binds to beta-1 receptors and
opens Ca-channels
•  This increases the rate of
depolarization during the
prepotential phase; HR increases !
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The Heart Beat: the conducting cells
•  Heart is stimulated
by the sympathetic
cardioacceleratory
center •  Heart is inhibited by
the parasympathetic
cardioinhibitory
center
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The Heart Beat: AP s in the contracting cells
The action potential of a
myocardial pumping cell.
The top graph shows the
action potential.
The lower graph shows what
happens to the ion
permeability of the membrane
during the same time.
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The Heart Beat: AP s in the contracting cells
The action potential of a
myocardial pumping cell.
The quick opening of voltagegated sodium channels is
responsible for the rapid
depolarization phase.
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The Heart Beat: AP s in the contracting cells
The action potential of a
myocardial pumping cell.
The quick opening of voltagegated sodium channels is
responsible for the rapid
depolarization phase.
The prolonged plateau of
depolarization is due to the slow
but prolonged opening of
voltage-gated calcium channels
PLUS
closure of potassium channels.
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The Heart Beat: AP s in the contracting cells
The action potential of a
myocardial pumping cell.
Opening of potassium
channels and closure of
the calcium channels
results in the
repolarization phase.
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